This invention relates generally to tunneling machines, and more particularly to tunneling machines having a rotary boring or cutting head for boring passages through soft rock, hard rock and minerals.
The digging of a tunnel through soft material, such as clay and soft rock, or only partially consolidated materials, has long been done by machines having a rotary cutting head having cutters which scrape and dig away at the material, which is then collected and removed rearwardly from the tunnel. However, when such machines are used against harder materials, and particularly very hard igneous and metamorphic rocks, such scraping-type cutters cannot be used, and it is necessary to employ rotary, percussive-type tools which chip away small fragments from the mass of rock by impact. The use of such cutters has long been known for drilling wells and other relatively small diameter holes, but efforts to adapt such cutters to larger machines for use in drilling tunnels have met with considerable difficulty because of the necessary forces involved and the shock loads encountered.
A reliable and proven machine has been developed for cutting hard rock at a fast enough cutting rate to make it competitive with prior drilling methods. That machine is set forth in U.S. Pat. No. 3,383,138. According to that patent, a fixed supporting frame is anchored in the tunnel by two axially spaced sets of projecting arms, each set of which has four arms equidistantly spaced and actuated by hydraulic cylinders to position the frame without regard to the weight of the machine. A movable frame is carried centrally within the supporting frame by sets of torque arms at each end, which both support the moving frame and transmit the reaction torque from the moving frame to the supporting frame. A cutter head is mounted in bearings at the front end of the moving frame and carries a cutter plate having a number of roller cutters mounted thereon. A drive shaft extends the length of the moving frame to project beyond the rear of the supporting frame where the shaft is driven by a plurality of motors which drive an encircling ring gear. Hydraulic cylinders acting between the supporting frame and the cutter head apply the force directly to the bearing supporting the cutter head to cause the moving frame to move relative to the supporting frame. After the moving frame is moved through its full range of movement, a jack is lowered at the rear end to support the moving frame by the jack and the cutter head to allow the supporting frame to have the arms retracted and moved forward to the next position, where the supporting frame is again anchored to allow the cutting movement to continue.
While such a tunneling machine can cut hard rock at a fast enough cutting rate to make it competitive with prior tunneling machines, contractors have demanded even faster cutting rates to minimize on-the-job dwell time and to meet contractual bidding demands. According to prior art practices, and as has been indicated above, a substantial portion of the available drilling time is expended in moving the gripping legs to an advanced position while the cutting head is idle at the tunnel face.